LIGO and Detection of Gravitational Waves

1. LIGO and Detection of Gravitational Waves Barry Barish 14 September 2000

2. Einstein’s Theory of Gravitation Newton’s Theory “instantaneous action at a distance” Einstein’s Theory information carried by gravitational radiation at the speed of light

3. Einstein’s warpage of spacetime Imagine space as a stretched rubber sheet. A mass on the surface will cause a deformation. Another mass dropped onto the sheet will roll toward that mass. Einstein theorized that smaller masses travel toward larger masses, not because they are "attracted" by a mysterious force, but because the smaller objects travel through space that is warped by the larger object.

4. Predict the bending of light passing in the vicinity of the massive objects First observed during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster Their measurements showed that the light from these stars was bent as it grazed the Sun, by the exact amount of Einstein's predictions. The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement of light as gravitational lensing.

5. Einstein’s Theory of Gravitation experimental tests “Einstein Cross” The bending of light rays gravitational lensing Quasar image appears around the central glow formed by nearby galaxy. The Einstein Cross is only visible in southern hemisphere. In modern astronomy, such gravitational lensing images are used to detect a ‘dark matter’ body as the central object

6. Einstein’s Theory of Gravitation experimental tests Mercury’s orbit perihelion shifts forward twice Newton’s theory Mercury's elliptical path around the Sun shifts slightly with each orbit such that its closest point to the Sun (or "perihelion") shifts forward with each pass. Astronomers had been aware for two centuries of a small flaw in the orbit, as predicted by Newton's laws. Einstein's predictions exactly matched the observation.

7. Gravitational Waves the evidence Neutron Binary System PSR 1913 + 16 -- Timing of pulsars 17 / sec · · ~ 8 hr

8. Hulse and Taylorresults emission of gravitational waves • due to loss of orbital energy • period speeds up 25 sec from 1975-98 • measured to ~50 msec accuracy • deviation grows quadratically with time

9. Radiation of Gravitational Waves Waves propagates at the speed of light Two polarizations at 45 deg (spin 2) Radiation of Gravitational Waves from binary inspiral system LISA

10. Interferometersspace The Laser Interferometer Space Antenna (LISA) The center of the triangle formation will be in the ecliptic plane 1 AU from the Sun and 20 degrees behind the Earth.

11. Interferometers terrestrial Suspended mass Michelson-type interferometers on earth’s surface detect distant astrophysical sources International network (LIGO, Virgo, GEO, TAMA) enable locating sources and decomposing polarization of gravitational waves.

12. Astrophysics Sourcesfrequency range Audio band • EM waves are studied over ~20 orders of magnitude • (ULF radio -> HE  rays) • Gravitational Waves over ~10 orders of magnitude • (terrestrial + space)

13. Interferomersinternational network Simultaneously detect signal (within msec) Virgo GEO LIGO TAMA detection confidence locate the sources decompose the polarization of gravitational waves AIGO

14. Detection of Gravitational Waves interferometry Michelson Interferometer Fabry-Perot Arm Cavities suspended test masses LIGO (4 km), stretch (squash) = 10-18 m will be detected at frequencies of 10 Hz to 104 Hz. It can detect waves from a distance of 600 106 light years

15. LIGO Ithe noise floor • Interferometry is limited by three fundamental noise sources • seismic noise at the lowest frequencies • thermal noise at intermediate frequencies • shot noise at high frequencies • Many other noise sources lurk underneath and must be controlled as the instrument is improved

16. LIGO Iinterferometer • LIGO I configuration • Science run begins • in 2002

17. LIGO Sites Hanford Observatory Livingston Observatory

18. LIGO Plansschedule 1996 Construction Underway (mostly civil) 1997 Facility Construction (vacuum system) 1998 Interferometer Construction (complete facilities) 1999 Construction Complete (interferometers in vacuum) 2000 Detector Installation (commissioning subsystems) 2001 Commission Interferometers (first coincidences) 2002 Sensitivity studies (initiate LIGOI Science Run) 2003+ LIGO I data run (one year integrated data at h ~ 10-21) 2005 Begin LIGO II installation

19. LIGO Livingston Observatory

20. LIGO Hanford Observatory

21. LIGO FacilitiesBeam Tube Enclosure • minimal enclosure • reinforced concrete • no services

22. LIGOBeam Tube • LIGO beam tube under construction in January 1998 • 65 ft spiral welded sections • girth welded in portable clean room in the field

23. Beam Tube Bakeout

24. Bakeoutresults

25. LIGOvacuum equipment

26. Vacuum Chambers BSC Chambers HAM Chambers

27. Seismic Isolation

28. Seismic Isolationconstrained layer damped springs

29. Seismic Isolation Systems Progress • production and delivery of components almost complete • early quality problems have mostly disappeared • the coarse actuation system for the BSC seismic isolation systems has been installed and tested successfully in the LVEA at both Observatories • Hanford 2km & Livingston seismic isolation system installation has been completed, with the exception of the tidal compensation (fine actuation) system • Hanford 4km seismic isolation installation is complete HAM Door Removal (Hanford 4km)

30. Seismic Isolation Systems Support Tube Installation Stack Installation Coarse ActuationSystem

31. LIGO Laser • Nd:YAG • 1.064 mm • Output power > 8W in TEM00 mode

32. Laser Prestabilization • intensity noise: • dI(f)/I <10-6/Hz1/2, 40 Hz<f<10 KHz • frequency noise: • dn(f) < 10-2Hz/Hz1/2 40Hz<f<10KHz

33. Opticsmirrors, coating and polishing • All optics polished & coated • Microroughness within spec. (<10 ppm scatter) • Radius of curvature within spec. (dR/R < 5%) • Coating defects within spec. (pt. defects < 2 ppm, 10 optics tested) • Coating absorption within spec. (<1 ppm, 40 optics tested)

34. LIGOmetrology • Caltech • CSIRO

35. Input Opticsinstallation & commissioning • The 2km Input Optics subsystem installation has been completed • The Mode Cleaner routinely holds length servo-control lock for days • Mode cleaner parameters are close to design specs, including the length, cavity linewidth and visibility • Further characterization is underway

36. Commissioning Configurations • Mode cleaner and Pre-Stabilized Laser • Michelson interferometer • 2km one-arm cavity • At present, activity focussed on Hanford Observatory • Mode cleaner locking imminent at Livingston

37. Schematic of system

38. CommissioningPre-Stabilized Laser-Mode Cleaner • Suspension characterization • actuation / diagonalization • sensitivity of local controls to stray Nd:YAG light • Qs of elements measured, 3 10-5 - 1 10-6 • Laser - Mode Cleaner control system shakedown • Laser frequency noise measurement

39. Wavefront sensingmode cleaner cavity • Alignment system function verified

40. Michelson Interferometer • Interference quality of recombined beams (>0.99) • Measurements of Qs of Test Masses

41. 2km Fabry-Perot cavity • Includes all interferometer subsystems • many in definitive form; analog servo on cavity length for test configuration • confirmation of initial alignment • ~100 microrad errors; beams easily found in both arms • ability to lock cavity improves with understanding • 0 sec 12/1 flashes of light • 0.2 sec 12/9 • 2 min 1/14 • 60 sec 1/19 • 5 min 1/21 (and on a different arm) • 18 min 2/12 • 1.5 hrs 3/4 (temperature stabilize pre modecleaner)

42. 2km Fabry-Perot cavity • models of environment • temperature changes on laser frequency • tidal forces changing baselines • seismometer/tilt correlations with microseismic peak • mirror characterization • losses: ~6% dip, excess probably due to poor centering • scatter: appears to be better than requirements • figure 12/03 beam profile

43. 2km Fabry-Perot cavity15 minute locked stretch

44. Significant Events

45. LIGO Ithe noise floor • Interferometry is limited by three fundamental noise sources • seismic noise at the lowest frequencies • thermal noise at intermediate frequencies • shot noise at high frequencies • Many other noise sources lurk underneath and must be controlled as the instrument is improved

46. Noise Floor40 m prototype • displacement sensitivity • in 40 m prototype. • comparison to predicted contributions from various noise sources

47. Phase Noisesplitting the fringe • spectral sensitivity of MIT phase noise interferometer • above 500 Hz shot noise limited near LIGO I goal • additional features are from 60 Hz powerline harmonics, wire resonances (600 Hz), mount • resonances, etc

48. Chirp Signalbinary inspiral determine • distance from the earth r • masses of the two bodies • orbital eccentricity e and orbital inclination i

49. LIGOastrophysical sources Compact binary mergers

50. LIGO Sites Hanford Observatory Livingston Observatory